Self-disarming electric blasting caps and assembly containing same



Dec. 5, 1967 H. E. DRIscol- L ET AI- 3,355,024 SELF-DISARMING ELECTRIC BLASTING CAPS AND ASSEMBLY CONTAINING SAME Filed Nov. 9, 1966 II |5 Il lsa/l FIG. 4

FIG.3

FIG. 2

FIG.

IN VENTORS FIG. 8

AGENT United States Patent O 3,356,024 SELF-DISARMING ELECTRIC BLASTING CAPS AND ASSEMBLY CONTAINlNG SAME Hiram E. Driscoll, Woodstock, and Pressley B. Miller,

Kingston, N.Y., assignors to Hercules Incorporated,

Wilmington, Del., a corporation of Delaware Filed Nov. 9, 1966, Ser. No. 593,012 14 Claims. (Cl. 102-28) ABSTRACT F THE DESCLSURE An electric blasting cap assembly is provided which is self-disarming after a preset time period of underwater emplacement allowed for completion of normal tiring. The assembly, preferably formed from a metal shell, contains (l) a material which forms an agent sufciently corrosive to the ring circuit and/ or the metal shell, upon contact with water, to break the circuit and/or disintegrate the metal shell to disarm the assembly and thereby render it harmless and (2) means for controlled rate of water ingress into the shell in contact with the corrosion agent-forming material to form corrosion agent for the disarming after the preset time. The invention also contemp-lates a complete explosive cartridge assembly containing the above cap assembly as the primary initiator.

This invention relates to electric blasting caps adapted to function normally for a predetermined period of time after emplacement in a Water-covered blasting environment but to thereafter become disarmed when remaining in that environment. In one aspect this invention relates to a complete explosive assembly particularly well adapted for seismic exploration in offshore areas, containing an electric blasting cap, above described, as a primary initiator. Other aspects will become apparent in light of the accompanying disclosure and claims.

A complete explosive assembly constitutes a combination of an explosive blasting composition together with means for initiating it. Such an assembly particularly applied to general blasting, seismic exploration and the like, generally comprises a cartridge containing a main capinsensitive explosive blasting composition such as a nitrocarbonitrate, or a dynamite, a secondary initiator, or booster, containing PETN, tetryl, RDX or the like as booster charge, and an electric blasting cap, as a primary initiator. The electric blasting cap contains a base explosive charge and electrically actuated means for initiating detonation of same. The booster charge is detonatable in response to the detonation of the base charge of the blasting cap and the main explosive blasting composition is detonatable in response to detonation of the booster charge to provide the full explosive force.

An electric blasting cap, utilized as a primary initiator, as above described, is either of the instantaneous or delay type and contains a base charge, a priming charge, an ignition composition, and electrical means for ignition of the ignition composition. The priming charge is detonatable in response to ignition of the ignition composition, and the base charge is detonatable in response to the detonation of the priming charge. In some instances a single composition functions initially as an ignition composition and then as a primer composition, but in all events the base charge is in operative communication with the ignition composition to detonate in response to ignition .of same. In a delay type electrical blasting cap, any suitable delay fuse composition, eg., barium peroxideselenium, or barium peroxide-tellurium is utilized in conjunction with separate ignition and primary charges. The fuse composition is disposed intermediate those charges to provide delay in detonation ot the primer after initiation of the ignition composition.

A typical and generally utilized secondary initiator assembly is a booster cartridge containing a high explosive such at PETN, RDX, tetryl, or the like, as a booster charge, and a well for supporting a primary initiator in operative communication with the booster charge so as to initiate detonation of the latter. The secondary initiator is generally supported in a well in the main charge of the assembly in indirect detonating relationship with the main charge for detonation of same.

In the emplacement of a complete explosive assembly in a water-covered area, it is often necessary that there be long lines of communication between the primary initiator of the assembly and the power source. There are also various support lines utilized in the handling of the assembly during its emplacement in the shooting area. It can be readily appreciated, therefore, that in the emplacement and firing of the assembly there will be from time to time failures of the system or damage imparted to the lead and communication lines, generally with loss of the assembly, the result in all events being a misliring, i.e. [failure to shoot due to loss of communication with the energy source. In many such instances of misiiring the assembly remains live, uncontrolled, and retrievable with great diiculty, if retrievable at all.

Misflring of assemblies in water-covered areas, and especially in areas of offshore seismic exploration presents serious safety hazards in respect toproperty, and persons in the adjacent shoreline area. In many such instances, the complete assemblies, or components separated therefrom, still live but out of control, are eventually washed ashore and are subject to accidental irings to impair the safety of the adjacent shore areas and of persons frequenting such areas who are unskilled in the art of explosives and who can be seriously injured in encountering the live elements, such as when endeavoring to handle them.

Offshore seismic exploration, in view of the misrings that occasionally occur at the shooting site, with concomitant washing ashore of lthe still live elements of the seismic explosive assembly that remain, has presented such hazards to shore areas that in some instances local government authorities have deemed it necessary to halt the exploration work taking place off their shores until there can be assurance that explosive assemblies or components thereof resulting from misirings will not impair the safety of their shore areas.

This invention is concerned with electric blasting caps as primary initiators adapted to function normally in a complete explosive assembly in Water-covered blasting areas for a predetermined period and to become disarmed after that time, to thereby be free from potential hazards of uncontrolled shots following misrings. The invention is particularly concerned with such initiators utilized in offshore seismic exploration assemblies.

In accordance with the invention, an electric blasting cap assembly is provided which comprises a closed elongated shell; a base explosive charge in one end of said shell disposed therein as described hereinafter; a dielectric ignition plug within said shell in closing relationship therewith and spaced from said base charge; a pair of leg wires longitudinally extending into said shell through the end thereof opposite said base charge in direct sealed contact with said dielectric plug, and terminating within said shell intermediate said base charge and said ignition plug; a bridge wire connecting the terminal ends of said leg Wires to thereby form an electrical circuit therewith, an ignition composition within said shell in direct contact with said bridge wire; said ignition composition being ignitable in response to heat from said bridge wire developed by passage of electric current through said circuit, and said base explosive charge being disposed in operative communication with said ignition composition to detonate in response to ignition of said ignition composition; a corrosion agentforming material within said cap assembly chemically inert to all components of said assembly but, upon contact with water, forming an agent corrosive to any of said wires in said circuit, and present in amount to form said agent in quantity to corrode any of said Wires sufiiciently to break said circuit; said corrosion agent-forming material being disposed within said assembly so as to permit direct contact of said corrosion agent, when formed, with said circuit for corroding same as described; ingress means in said cap assembly for admitting water from outside said shell into contact at a rate, and in an amount, with said corrosion agent-forming material to form said agent for said corrosion so as to break said circuit after a preset period of water ingress time, whereby said blasting cap assembly becomes disarmed.

In the practice of one form of the invention, the corrosion agent-forming material functions as a `porous top end closure plug for the cap shell, either alone, or dispersed in a porous carrier, generally in direct communication with the outside of the shell. Ingress of water is provided by the porous state of the closure plug or by one or more passageways in direct communication with the closure plug and disposed in the side wall of the shell or in a top end protective member when one is utilized as described hereinafter. The porous -plug closure is disposed in the top end of the shell, i.e. opposite that containing the base charge, and is generally superposed on the dielectric ignition plug. It is in direct contact with bared sections of the leg Wires as they extend into the shell. In another form of the invention the corrosion agent-forming material is dispersed in one or more of the ingredients in the ignition area of the assembly, i.e. containing the base, primer and ignition charges, and one or more passageways are disposed in the side wall or end wall (bottom) of the shell in direct communication with that area for the necessary water ingress.

In accordance with one embodiment, the shell of the electric blasting cap is metallic and the corrosion agent, formed as described, is also corrosive to the metal shell. Sufficient corrosion agent-forming material is present in the assembly to form corrosion agent to also corrode the shell to cause it to at least partially disintegrate. The water ingress means is adapted to admit water into the shell, in an amount and at a rate, for the formation of corrosion agent to additionally effect the desired corrosion of the shell wall after the preset period. This embodiment provides for disarming by not only breaking the electrical circuit, but also by disintegrating the shell so that the explosive ingredients therein will be dispersed, or washed, into the surrounding water environment.

Another embodiment of the invention provides for electrolytic action to accelerate corrosion of the shell. In the practice of this embodiment the cap shell is metallic and it contains any suitable metal member, formed from a metal dissimilar to that forming the shell. The metal member, such as a metal strip, or a capsule element described hereinafter, is in Contact with the inner shell wall and is disposed so as to be in direct communication with the corrosion agent when formed. In this manner, upon ingress of Water into the shell to form the corrosion agent, an electrolytic reaction is set up between the two dissimilar metals to accelerate the rate of corrosion of the shell.

Now preferred practice involves a combination of the above embodiments, including the presence of sulfur as a top plug closure seal for the shell and also as a dispersion in diazodinitrophenol, in the ignition area, as a single ignition-primer composition. A single passageway for water ingress is in the bottom of the shell. The shell is metallic and contains a capsule type retainer for a lportion of the diazodinitrophenol composition, the capsule being formed from a metal dissimilar to that forming the shell to accelerate corrosion of the shell by electrolytic action, described above. In this preferred practice, the dissimilar metals are of the group of copper, bronze and aluminum. The shell is generally formed from aluminum and the capsule is generally formed from bronze or copper.

When referring herein to a wall of the blasting cap shell, it is meant to include not only a side wall of the shell but also an end wall, the latter also referred to herein as the bottom of the shell.

The invention is illustrated with reference to the drawings of which FIGURE l is a cross-sectional view of an electric blasting cap of the invention in which sulfur, as the corrosion agent-forming material, forms a topmost closure member; FIGURE 2 is another cross-sectional view of an electric blasting cap of the invention in which sulfur, as the corrosion agent-forming material is dispersed in the ignition area, utilizing diazodinitrophenol as a single ignition-primer composition; FIGURE 3 is the same as FIGURE 2 except that a lower portion of the ignition-primer composition is disposed within a capsule, and the capsule and blasting cap shell are formed from dissimilar metals for purpose of electrolytic reaction to accelerate corrosion of the cap shell; FIGURE 4 is the same as FIGURE 2 except that separate primer and ignition compositions are utilized; FIGURE 5 is the same as FIGURE 4 except that the topmost closure plug is formed from sulfur, as in FIGURE l, and there is no other corrosion agent-forming material in the assembly; FIGURE 6 illustrates now preferred structure which is a combination of that of FIGURES 1, 2 and 3; FIGURE 7 illustrates an often utilized structure of the invention which is a combination of that of FIGURES 4 and 5; and FIGURE 8 illustrates a complete explosive assembly containing an electric blasting cap of FIGURE 6 as a primary initiator and particularly well applied to offshore seismic exploration. In the drawings, like numbers among the various figures refer to like parts and primed numbers refer to parts corresponding to those of the same number unprimed.

Referring to FIGURE 1, elongated bronze, copper, or aluminum, shell 9 of blasting cap assembly 10 is closed at bottom end 11. Electrical conductor wires, i.e., leg wires, l2 extend longitudinally into shell 9 through top sulfur closure plug 13 in end 14, dielectric ignition closure plug 16, and impact disc 17 into primer-ignition composition 18, advantageously diazodinitrophenol. Electrical resistance, or bridge, wire 19 connects the terminal ends of leg wires 12 in primer-ignition composition 18 to form a resulting tiring circuit for initiating ignition of compositon 18, and leg wires 12 are electrically insulated by insulation 21, as they extend into shell 9 and closure plug 13 but are uninsulated, or bare, along a portion of their length as they extend through sulfur plug 13, i.e., generally from a point near the top end thereof toward bridge wire 19.

Impact disc 17 serves to isolate ignition plug 16 from primer-ignition composition 1S. Base charge 23, such as PETN, tetryl, RDX, or the like, in shell 9 is in the end section of shell 9 containing end 11. Primer-ignition mixture 18 is superposed on base charge 23, ignition plug 16 is superposed on primer-ignition mixture 18, separated from direct contact therewith only by impact member 17, and top closure 13 is superposed on ignition plug 16.

Diazodinitrophenol, as primer-ignition mixture 18, serves as both ignition and primer. It is pressed in a bottomrnost portion, adjacent base charge 23, to a degree less than that of the remaining portion around bridge Wire 19 so that it can ignite in response to heat from bridge wire 19 developed by passage of electric current through the firing circuit, and then detonate at its lower state of press in response to the initial ignition. Base charge 23 is then detonatable in response to detonation of the primer ignition composition 1S.

In this embodiment, sulfur closure plug 13, in direct communication with the outside of the shell, is of sutilcient porosity to provide for ingress of water into the cap assembly through the top end 14. Sulfur closure plug 13 reacts with the incoming water from outside the shell 9 to form reaction product corrosive to leg wires 12 and to the shell wall to break the firing circuit and/or to at least partially disintegrate the shell to thereby totally disarm the assembly.

With reference to FIGURE 2 is shown assembly 10a which is the same as assembly of FIGURE 1, except that, in lieu of top sulfur closure plug member 13, a dielectric top closure 13', devoid `of a corrosion agentforming material, is sealed in closing relationship with the inner wall of shell 9 and with leg wires 12; bottom end 11 of shell 9 contains a passageway 15 extending longitudinally through end 11 to provide for ingress of water from outside shell 9 into the shell interi-or; and primer-ignition composition 18 contains sulfur dispersed throughout as the corrosion agent-forming material in accordance with the invention.

Passageway 15 is of size to permit ingress of a sufiicient amount of water, and at a rate, into shell 9, to penetrate base charge 23 and primer-ignition 18 to react with sulfur in composition 18' and form the requisite amount of corrosive reaction product to Contact wires 12, bridge wire 19, and the shell inner Wall to corrode those members to the extent -of severing at least one of the leg Wires 12 or the bridge wire 19, and/or to cause at least partial disintegration of the wall of shell 9 to permit dispersing of the contents of the shell into the surrounding water environment. By either or both corrosive actions, self-disarming of the cap assembly takes place.

With reference to FIGURE 3 is shown assembly 10b which is the same as assembly 10a of FIGURE 2 except that a hollow cylindrical aluminum, copper or bronze capsule 2t) is superposed coaxially in shell 9 on base charge 23 and extends upwardly into about the bottom 1A to 1/2 of primer-initiator composition 18', its terminating end in composition 18' being in reduced diameter equal to about 1/2 to 3%; of the inside diameter of shell 9. Capsule serves one or both of two functions, as desired. In the first place it serves to protect a lowermost portion of composition 18', i.e., adjacent base charge 23, from undue press during fabrication of the assembly, which can result when the ignition plug 16 and iiring circuit unit of the assembly is pressed into superposed position on composition 18. Capsule 20 facilitates control of the degree of press in the lower portion of Composition 18 which in all events is necessary to maintain that portion of the ignition-primer detonatable in response to ignition of the remaining upper and denser portion which, in turn, occurs in response to heat from the bridge wire of the firing circuit. Secondly We have discovered that when capsule 20 is formed from a metal dissimilar to that of the metal forming shell 9, and water is admitted from outside the shell, into contact with the corrosion agent-forming material, there is electrolytic action in the presence of the resulting corrosion agent with an accompanying acceleration of corrosion rate of the shell.

With reference to FIGURE 4 is shown an electric blasting cap assembly 30, comprising shell 9, closed bottom end 11, a passageway 1S, base charge 23, a top closure 13', ignition plug 16 and leg wires 12 with insulation 21, all as shown with reference to FIGURE 2. Leg wires 12 terminate in ignition composition 31, which can be any suitable composition such as lead-selenium, lead mononitroresorcinate, or the like, and are connected therein by bridge Wire 19. Assembly 30 contains semiconductive plug 32, eg., aluminum dispersed in Wax, as a closure for shell 9 intermediate ignition mixture 31 and ignition plug 16. Plug 32 is stepped inwardly along its lowermost end portion. Sleeve 33, coaxially Within shell 9 extends along the wall of shell 9 adjacent ,the stepped in portion of plug 32 and beyond plug 32 to a distance to provide a cavity in which ignition charge 31 is disposed. Priming charge 34, advantageously diazodinitrophenol, in shell 9 of assembly 30 is superposed on base charge .23 and ignition mixture 31 is intermediate primer 34 and plug 32 and superposed on primer 34 within the contines of the cavity formed by that portion of sleeve 33 extending downwardly from plug 32.

Sulfur as the corrosion agent-forming material is dispersed through either the ignition composition 31 or primer 34, as desired, and is reactable with Water admitted from outside shell 9 through passageway 15 in the end wall of the shell to form reaction product for effecting corrosion of bridge wire 19 and/'0r one or both of the terminating ends of Wires 12 in ignition mixture 31, and/ or the metal shell.

With reference to FIGURE 5 is shown assembly 30a which is the same as that of assembly 30 of FIGURE 4 except that it contains ignition composition 31', in lieu of ignition 31 of FIGURE 4, top closure plug 13 in lieu of closure 13' of FIGURE 4, i.e., formed from sulfur, and the end 11 of shell 9 is completely closed. Ignition composition 31' is free from a corrosion agent-forming material of the inventi-on. Disarming of assembly 30a takes place by reaction of Water admitted into closure plug 13 for the formation of corrosive reaction product as described with reference to FIGURE 1.

With reference to FIGURE 6 is shown a now preferred assembly 10c which is a combination of assemblies 10, 10a and 10b of FIGURES 1 3. Assembly 10c is the same as assembly 10b of FIGURE 3 except that it contains a top closure 13 of assembly 10, i.e., formed from sulfur, in lieu of closure 13 of assemblies 10a and 10b, Assembly 10c by virtue of an additional area ,for contact of water and the corrosion agent-forming material is generally self-disarmed more readily than when there is yonly one such corrosion agent-forming reaction area in the assembly. This embodiment, i.e., assembly 10c, is particularly advantageous when disarming is required in rather shallow water covered areas such as for example when the hydrostatic head is in the order of only a few p.s.i., e.g., from 2-5 p.s.i.

With reference to FIGURE 7 is shown an often utilized embodiment of the invention, viz assembly 30]), which is the same as assembly 30 of FIGURE 4 except that it contains a top closure 13 of assembly 30 of FIG- URE 5, in lieu of the sulfur free top closure 13 of FIG- URE 4. Disarming of assembly 30!) occurs in the manner as described herein above with reference to assembly ltlc of FIGURE 6, both assemblies containing two reaction product-forming areas.

With reference to FIGURE 8 is shown a complete explosive assembly containing a primary initiator, i.e. an electric blasting cap of this inventori, connecting with long communication lines utilized in offshore seismic operations. The complete explosive assembly 40 comprises elongated cartridge shell 41 containing booster well 42 extending coaxially into shell 41 through top end 43 and adapted to accept a conventional booster 44 containing a charge of a high explosive, say in the order of about 25 grams of PETN, tetryl, RDX or the like. A primary initiator of this invention, preferably assembly c of FIGURE 6, is supported in cap well 46 of booster 44. Shell 41 contains a main explosive blasting charge which substantially fills shell 41 and, in all events, is in detonating relationship with the primary and secondary initiator system, viz booster 44 and blasting cap assembly 10c.

Also shown are lead lines 47, connecting with leg wires 12 of assembly 10c and with a shot firing cable 48 leading to the energy or power source, in many instances up to 100 yards or more distant.

When a misring occurs, and assembly 40 is lost, the assembly sinks to the bottom of the water area and after some time is, due to the various water movements. washed from one point to another and in many instances at ultimately the shoreline. 1n the process of being washed about, the still live initiators are often dislodged from the assembly, but often either the assembly, intact, or one or more of the dislodged live components reach the shorelines with the accompanying safety hazards. During the normal operating time water finds its way into the cap well 46 of booster 44 of assembly 10c, i.e. between the inner wall of well 45 and the outer wall of assembly 10c therein as well as on the top of assembly 10c. As provided by the invention, water gains access through passageway 15 and/or through the top sulfur closure member of assembly 10c into the interior of shell 9 to effect reaction with the sulfur leading to corrosion and self-disarming described hereinabove. The reaction is adapted to proceed initially but at a rate to allow for normal operation which is generally up to about one hour. Disarming occurs at any time after that preset period as desired, often within a matter of a few hours up to a month or longer. Whether subsequent to a misiire there is a separation of the complete explosive assembly 40 into the components, or whether the said assembly remains intact is immaterial. In any event the live primary initiator component becomes disarmed and thereby harmless and free from hazards normally involved when such live assemblies reach the shore and are handled by persons unskilled in the handling of explosives.

Further exemplary of suitable corrosion agent-forming materials utilized in the practice of the invention are dry solid acidic materials such as sodium acid sulfate, ferric chloride, ferrie sulfate, cuprous sulfate, calcium chloride, oxalic acid, fumaric acid, picric acid, zinc acetate and the like, all of which are chemically inert to all components of the blasting cap assembly and, upon contact with water, form a corrosion agent in the practice of the invention. The corrosion agent-forming materials are those which either (l) react chemically with water to form resulting reaction product which serves as the corrosion agent, or (2) form an aqueous solution of the material, the resulting solution serving as the corrosion agent. For example, sulfur reacts with water to form a highly acidic reaction mixture which serves as a corrosion agent whereas water dissolves oxalic acid to form a resulting aqueous oxalic acid which serves as the corrosion agent.

The corrosion agent-forming material disposed in the ignition area can be dispersed in one or all of the components therein, i.e. in the ignition, priming, or base charges, except that when the ignition composition is of the matchhead type the corrosion agent-forming material is preferably disposed in the priming or base charge, preferably the former.

The corrosion agent-forming material constituting the top end closure plug of the shell, such as a plug 13 of FIGURES 6 and 7, is generally sulfur, due to the ease of its emplacement in molten state and the porosity of the resulting solid plug which permits water ingress into the shell through the top end thereof. However, others of the corrosion agent-forming materials can be used as the top end closure plug when desired. Depending upon the particular corrosion agent-forming material it can be pressed into the cap and serve in the same manner as illustrated elsewhere with reference to sulfur closure plug 13 of the drawings. However the material can be dispersed in a porous inert carrier such as, for example, a clay and the resulting plug can serve in the same manner as illustrated with reference to sulfur plug 13. In some instances sulfur containing from about 1 to 5 weight percent of another corrosion agent-forming material is advantageously utilized as a top porous plug closure. If the corrosion agentforming material is highly water soluble, it can function as the top end closure in conjunction with a protective layer of waterproofing material at the top as for example a resin disc in watertight closing relationship with the shell. In such practice, or at any time desired, one or more passageways in the wall of the shell, in direct communication with the corrosion agent-forming top closure material, constitute a suitable water ingress means therefor. The size and number of such passageways is necessarily correlated with the corrosion agent-forming material to provide the requisite amount and rate of corrosion to accomplish disarming after the preset period.

The amount of corrosion agent-forming material in the cap assembly is dependent upon, and necessarily correlated, with the particular material and the amount of corrosion agent required. Generally, however, about 0.5 to 10 weight percent of the corrosion agent-forming material based on any one of the compositions in the ignition area is sufficient. Mixtures of corrosion-forming materials can generally be utilized in any suitable proportions. When dispersed in an inert porous carrier and serving as a top closure plug as described above, the proportion of corrosion agent-forming material is somewhat greater, say up to about 50 percent or higher.

It is generally necessary that the area of the total passageway means in direct communication with corrosion forming material in the ignition area is within the range of that of a circle having a diameter of 0.010 to 0.050 inch. In preferred practice one such passageway is utilized in the end wall of the shell as illustrated with reference to the drawings, although a plurality of such passageways can be utilized and located as desired, so long as they directly communicate with the particular corrosion agent-forming material and provided the total passageway area is within that required for the desired rate and amount of water ingress.

When referring herein to a preset period for normal firing of the electrical blasting cap of the invention, under water, it is meant a period generally not longer than about one hour, often from about 10 to 2O minutes. In all events the capacity of the water ingress means in either or both of the areas containing corrosion agentforming material, is correlated with the particular components of the assembly to deliver the necessary amount of water for the formation of the required amount of corrosion agent material during a time period greater than that preset for normal operation.

The leg wires and bridge wire of the firing circuit of the cap assembly of the invention can be any of those well known in the art. Leg wires are advantageously formed from about #20 to 22 copper or iron wire. Any of the well known alloy nickel type bridge wire materials for the firing circuit are particularly suitable.

Exemplary ignition primer and base charge components of the blasting cap assembly of the invention are any of those well known in the art. Diazodinitrophenol is particularly advantageously utilized as a primer-ignition composition with pressed PETN as a base charge. However, any of the well known ignition, primer, and base charge materials can be utilized.

Electric blasting caps A and B referred to in the following examples are those of FIGURES 6 and 7 respectively of the drawings yand are further characterized as follows:

closure or in the ignition area to cause disarming, or to impair normal tiring. Very little variation in resistance was observed among the assemblies, thus indicating that not only no disarming occurred during that period 5 but that there was no significant parallel shorting Electric Blasting Cap A Electrlc Blasting CapB across the lead wires to alter the intended conductive (FIGURE 6) (FIGURE 7) path along the circuit. These tests, summarized in the following tabulation, illustrate that a water-reactable ma- (1) 92 (lel 51161191 Sam@ as for terial, e.g., sulfur can be utilized in the practice of the in- Length-ov'erau, 1.97";.1ower 10 vention without impairing normal performance of the 590mm'105'(be1W1mPaCt blasting cap during a preset period under water. disc).

Outside Diemeter-upper see- Each cap was then shot, at the end of the one hour m0153285@ W Sectio, (preset) period, in accordance with the standard 1" x 0.278 1 (2) Bae Ch%rge23:1PETlI1\l- ,I @CBe Charge 23: Same as for 1 kX tlllCk lead plate CS and, aS s'l'lOWIl, all ShOS weig t,0.4 grain; engt 0.35 ap (a) Met-a1 capsule 20; (s) Primerai: 15 were successful' Ilg. 0 484 DgzodlmtrophenOI/Sulfur, TABLE 1,-REsISTANCE VARIATION OF CAP B (FIGURE 6) Outsidti Diameter-overall, Weight, 0.26 gram.

0.250; reduced, 0.242". Resistance, Ohms (4) Primer ignition charge 15': (4) Ignition composition 31; Plate Test After Diazdintrophenol (1d azol), l- 20103 L 20 Before Contact After Contact the 1 Hour Period ggkty 0.51 gram engt y Leeiliggth, with the Water with the Water* Stllur, 0.0 gran; uniformly Y lSpeI'Se 1n laZO. (5) ignition Plug i6; (5) sleeve a3; 1-20 1-26 A1 Bakelite. Paper. 1- 22 1- 27 A0 Length, 0.42". Length, 0.250". 1- 12 1-11 A1 Inside Diameter 0.205. L 21 1 29 AU (6) Top Closure Plug: (6) Semiconduetive Plug 32: 1- 25 1- 29 Ao Sulfur.2 Aluminumdispersed in wax.5 Length' 0375, Length X damtef-Tog Variation is within experimental error.

590mm (n.25 X 023,0 i A= Good shot, subscript number designates diameter of hole in plate rgover section, 0.125 x in millimeters' (7) Le Wires 12; Copper, #20. (7) Ignition'Piug 16: Exam le 2 g Eakelile. 4U H 30 p (8) Bridge Wire 19, (g) Tggglsfrepiug 13c Two separate series of 10 electric blasting caps A (FIG- T9DhetC" Same aSfOf Cap A URE 6) and B (FIGURE 7) were placed in salt water Diameter, 0.002. Length, 0.44. 5 d 2 Lengthy 0.075", under a hydrostatic head of 0. p.s.1.`for per1o s up to (9) Palegyvay 152 Diameter, @CIIJBsAWHeS 121 Same 2S for months. The resistance of the firing circuit of each of the (l0) rlge Wim 19'; 35 10 caps of each series was monitored weekly. The results Gold plated tophetC. are summarized in the following tabulation. As shown, Diameter, 0.002.

after 2 days of underwater exposure the electrical resis- 1 Loose iri capsule for detonation; pressed above capsule for ignition. tance of the blastmg caps A began t.0 dcrease mdlcatlng gEmpladln molten Slam 40 development of a parallel short circuit or, conductive 3 Uniforinly distributed in diezo. 4 Lead inononitroresorcinate/potassium chlorate buttered ln sleeve 33. path acl-.OSS .the leg wlres as a.resu1t of corrosion. effects .4i/candeline wex/niarasperse so.0/19.7/0.3. on the circuit caused by reaction of water, entering the E l I assembly from outside the assembly, with sulfur in the wmp e sulfur-containing areas. After 4 weeks the tests involving Five electric blasting caps B (FIGURE 7) were placed Caps B gave the same indication as shown by the deunder water for one hour at a hydrostatic pressure head creases in resistance observed. In tests of both series after of 5 p.s.i., after which time the resistance of the ring 6 weeks in the water, about half of the circuits were decircuit of each, formed by the bridge and leg wire was stroyed and after 2 months in the water -all of the circuits measured to determine if during that one hour period of the Caps A were destroyed with 80% destruction of there had been ingress of Water into the assembly sufv those circuits of the Caps B. ciently to react with the sulfur in either the sulfur seal 00 The results of these tests are tabulated as follows:

TABLE 2.-RESISTANCE, OHMS Electric Blasting Cap A Sample No.

ODays 2Days 2Weeks 3Weeks 4Weeks 6Weeks 2Months 0. 97 0. 72 0. 7i 0. 7i 0. 5s o. sa 0. 92 0. 56 0. 58 0. 70 0. 34 3. 63 0. 02 0. 9s 0. 83 0. 2s 0. 28 0. 46 0. 95 0. 9e 1.00 4. 32 0. 94 o. 4i 0.94 0. 90 0. 50 0. 85 0. 74 0. s0 0. 35 0. 5s 0. 47 0. 53 (r) 0. 90 0. s6 0. s0 0.61 1. 02 (ff) 0. 0s o. 64 0. 94 0.47 0. 62 ('f) 1.00 1.51 1.00 o. 89 0. 40 0.95 0. 3. 50 0. 50 (ff) Electric Blasting Cap B 1.10 i. 25 1.15 2. 59 1. 69 0. 87 0. 43 1. 25 1.15 1.08 1.00 1. 25 0. 75 0. 50 1.05 2.10 1. 25 1. 21 1. 0s 1. 05 1. 05 1.52 1.15 1.44 1.13 0. 9s 1.20 1. 1. 25 1. 27 1.18 1.17 (r) 1. 55 1.20 1. 26 0. 96 1. 02 1. 04 1. 20 1.15 1. 55 1.12 i. 25 (e) 1.05 1.55 1.17 1.25 1.21 1.05 1.30 l 1.30 1.22 1.07 1. 45 1.15 1. 75 1.10

* Leg wire corroded oi in top sulfur seal. Bridge wire corrosion not observed.

1 1 Example 3 In the order of about 100 each of Caps A and B were maintained under salt water for periods up to 7 Weeks 12 As shown in the above table, after 5 weeks under water the 5 caps tested, of each of the two sets, were completely disarmed as a result of corrosive action of the sulfurwater reaction product on at least one of the leg wires in under a hydrostatic head of 2 p.s.i., and 5 of each set were 5 the Sulfur Seal area subjected to the plate tests of Example 2 at weekly inter- Subsequent to the 5 week period no further plate tests vals through a S-Week period. At the end of 7 Weeks the were made. However, at the end of 7 weeks the remainder remainder of the caps were tested for resistance of the of the caps were inspected and, as shown above, of 78 ring circuits. The results of these tests are summarized remaining Caps A the circuit in 74 caps was broken by inthe following tabulation. lo corrosive action of the sulfur-water reaction product on one or more of the wires in the electric circuit. The 4 TABLE 3 remaining Caps A were made ineffectual by corrosive action resulting in a parallel circuit formed by the leg Plate Test Results wires in the sulfur seal area. Of the remaining 79 Caps B Time (Weeks) 15 the circuits in l0 were severed by corrosive action and 66 Caps A Caps B contained a parallel circuit between the lead Wires that would cause failure thereby becoming intfectual and 5A, 5A, harmless. gg, gg, gFl Of the circuits shown in Table 3, those in which a 1D: 4F11 4D: i 20 parallel short circuit was formed would ultimately have 5F.2 5F.z become completely disarmed by destruction of the circuit resulting from corrosive action of sulfur-water reaction Electmal Reslslance T555 0f the Firing Circuits product. However, in these instances the rate of corrosive Remaining Caps action of the sulfur-water reaction product on the metal 7 P Circuitsbmken by N Circuitsbmken by 25 shell was found to be greater than that of one or more eerrosien. corrosion of the wires in the circuit. 4-Al1 circuits of low (iQ-Circuits not broken:

resistance would fail 1, normal resistance; Example 4 d ue t o shorting of firing 2, high resistance; 66, www lfw eslsae wofudpfail About 2S each of Caps A and B were maintained in salt CU o mg mg 30 water under a hydrostatic head of 25 p.s.i. for various periods of time up to 389 hours to determine the corrosive IHA pemiieicireuii, tmmd 1i y arg1-esten, between the ieg wires, in the effect of the sulfur-water reaction production on aluminum su ur top se area, cause t e e' ures.

zwke severed by corrosion in the sulfur top Seal ma cap she 1 walls as well as on the leg wires in the sulfur snorting vie pereiiei circuit, roi-med by corrosion, between the eonseal area. The results 0f these tests are tabulated as fol ductor wires ln the sulfur top seal area. 35 lows:

TABLE 4 Electric Blasting Caps A Electric Blasting Caps B Time Time Number Under Firing Circuits Shells-Visual Effects Number Under Firing Circuits Shells-Visual Eiects Tested Water Tested Water (hrs.) (hrs.)

25 68 All normal Brown stain on out- 25 68 All normal 1 base separated from main side wall.l body by corrosion (at interface of base charge and primer). 104 dol 24 s? .do D0. 25 126 do 23 109 .do Qholes in shell in primer and ignition plug areas; 14 normal. 25 150 8 corroded in sulfur 23 133 do 12 holes in shell in primer and top seal area. ignition plug areas; 11

normal. 25... 173 10 ignition plug, ex- 23 156 do 17 holes in shell in primer and posed through wall. ignition plug areas; 6

normal. 25 244 .do 14 badly corroded. 23 227 do Do. 25. 406 i3 normal; 12 11 corroded in sulfur 23 389 16 normal; 7 6 normal except slightly cor circuit broken.2 top seal aren; 3 circuit broken.a roded at top of shell; 1 igniliadly corroded in tion plug lost through corsulfur top seal roded wall; 6 ignition plug area. and sulfur area exposed through wall; 5 completely corroded away at ignition plug and top sulfur plug areas.

l Stain due to presence of diazo, fr 2 8one lead wire broken; 3-both lead wires broken;

3 7one lead wire broken.

This example illustrates the short period of time required for action of corrosive reaction product to disarm an electric blasting cap in practice of the invention, whether by action on one or more of the wires of the firing circuit, or on the shell wall, or on both. As will be appreciated, given more time, all caps of this example would eventually have been disarmed by breakage of the firing circuit due to the corrosive action on one or more of the circuit wires. As was illustrated with reference to EX- ample 3, the corrosive action on the metal shell wall may often be at a higher rate than that on one or more wires in the tiring circuit depending on the particular corrosive agent and the wire and shell compositions. In this series of tests, had there been more time for corrosive action the circuits would have been broken except in those instances wherein the corrosion of the shell wall would have been so extensive that the contents of the cap shell would have been washed from the assembly before breaking of the circuit.

Example Three sets of about 50 electric blasting Caps B each, were placed in saltwater at room temperature for different periods of time up to 72 hours, and then stored at 120 F. for periods up to 2 months. The results of these tests are summarized as follows:

GC=Good Circuit.

NC=N0 Circuit.

All caps were circuit tested prior to the above tests and were found to have good circuits.

The numeral shown above and identified with results of each test (GC, NS) designates the number of caps that were tested after each period of storage time. Each test involved a different group of caps of the particular set.

Each cap showing no circuit (NC) was visually inspected to determine the cause of the circuit failure. In each instance the NC was found to be the result of corrosion of at least one joint connecting the bridge wire and leg wires.

In one form of now preferred practice, diazodinitrophenol, as the primer-ignition composition contains from about 1 to 5 percent of its weight of sulfur as the corrosion agent-forming material and alternatively, it can also contain, together with the sulfur, from about 1 to 3 percent of its weight of another corrosion agent-forming material of the class of solid acidic materials such as those illustrated hereinabove. In this practice, the water ingress means is generally a single passageway in the shell wall in direct communication with either the base charge or the primer-ignition composition, being generally disposed in the bottom end of the shell and having an area equal to that of a circle having a diameter of at least 0.010 inch but not exceeding about 0.025 inch.

Any suitable method can be utilized in the fabrication of an electric blasting cap assembly of the invention. In accordance with one procedure the base charge is pressed into a closed end of an elongated metal shell containing a passageway for water ingress as illustrated with reference to the drawings. A capsule member such as illustrated with reference to the drawings (capsule is then placed in the cap shell on the base charge. Diazodinitrophenol (diazo) containing from about 1 to 5 weight percent sulfur as a primer-ignition composition is placed in the shell on the capsule and by vibratory action a portion is caused to settle in the capsule. The combined ignition plug and the ring circuit, i.e. the leg Wires extending through the plug and terminating with connecting bridge wire, is pressed into the shell, bridge wire first, to dispose the bridge wire within the diazo and press the diazo. The capsule serves to protect the portion of diazo therein from undue press. In this manner the diazo in the capsule is Vless dense than the portion above the capsule so that that portion above the capsule ignites in response to heat from the bridge wire and the remaining or lower portion detonates in response to the ignition. Molten sulfur is then poured into the shell onto the ignition plug and around leg wires extending upwardly from the ignition plug to form a top closure member for the shell. The leg wires are uninsulated along a portion of their length in contact with sulfur as illustrated with reference to the drawings. A corrugation is disposed around the shell near the top end to serve as an anchoring member to support the sulfur seal in place (see corrugation 25 of the drawings). An assembly formed as above described is illustrated with reference to FIGURE 6 of the drawings. By obvious modifications of the above procedure, other cap assemblies of the invention can be formed.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What we claim and desire to protect by Letters Patent is:

1. An electric blasting cap assembly capable of selfdisarming after misring in a Water environment, which comprises a closed elongated shell; a base explosive charge in one end of said shell disposed therein as described hereinafter; a dielectric ignition plug within said shell in closing relationship therewith and spaced from said base charge; a pair of leg wires longitudinally extending into said shell through the end thereof opposite said base charge in direct sealed contact with said dielectric plug, and terminating within said shell intermediate said base charge and said ignition plug; a bridge wire connecting the terminal ends of said leg wires to thereby form an electrical circuit therewith; an ignition composition within said shell in direct contact with said bridge wire; saidignition composition being ignitable in response to heat from said bridge wire developed by passage of electric current through said circuit, and said base explosive charge being disposed in operative communication with said ignition composition to detonate in response to ignition of said ignition composition; a corrosion agent-forming material within said cap assembly chemically inert to all components of said assembly but, upon contact with water, forming an agent corrosive to any of said wires in said circuit, and present in amount to form said agent in quantity to corrode any of said wires sufficiently to break said circuit; said corrosion agent-forming material being disposed within said assembly so as to permit direct contact of said corrosion agent, when formed, with said circuit for corroding same as described; ingress means in said cap assembly for admitting water from outside said shell into contact at a rate, and in an amount, with said corrosion agent-forming material to form said agent for said corrol sion so as to break said circuit after a preset period of 3. In a blasting cap assembly of claim 2, a metal member in said assembly dissimilar to that forming said shell, and in contact with the inner wall of said shell; said metal member and said inner shell wall in contact therewith being disposed in communication with said corrosion agent-forming material so as to both be directly contacted by said corrosion agent when formed as described.

4; Inv an assembly of claim 2, a corrosion agent-forming material as a closure plug, in the end of said shell opposite said base charge, and in direct communication with the outside of said shell; and said closure plug havingA suiicient porosity to provide for sole ingress of water f or contact therewith to form said corrosion agent.

5. In an assembly of claim 2, said corrosion agentformingA material dispersed in the ignition area of said cap assembly; and a passageway in a wall of said shell, in directv communication with said ignition area to provide for saidr water ingress.

6. In an assembly of claim 2, diazodinitrophenol as a combined primer-ignition charge, and sulfur dispersed therein as said corrosion agent-forming material; a cylindrical member, coaxia-l with said shell and disposed around a portion of said diazodinitrophenol adjacent to said base charge, and in contact along its outer surface with the inner wall of said shell; and a passageway in a wall of said shell, in direct communication with said corrosion agent-forming material to provide for said water ingress.

'7. An assembly of claim 2 containing separate ignition and primer charges, and at least one of said ignition and primer charges containing said corrosion agent-forming material; and a passageway through a wall of said shell in direct communication with said material to provide for said water ingress.

8. An assembly of claim 2 containing diazodinitrophenol as a combined ignition-primer charge, and said charge containing said corrosion agent-forming material; and a passageway in the end of said shell adjacent to said base charge, to provide for said ingress of water.

9. An electric blasting cap comprising a closed elongated metal shell; a base explosive charge in one end of said. shell; a dielectric plug in said shell in closing relationship therewith and spaced away from said base charge; diazodinitrophenol in said shell intermediate said base charge and said dielectric closure plug, as an ignition-primer charge, and containing from about 1 to 5 weight percent sulfur dispersed therein; a pair of leg Wires longitudinally extending into said shell through the end thereof opposite that containing said base charge and then through said. dielectric plug, and terminating in direct contact with said ignition-primer composition; a bridge wire in said shell connecting the terminating ends of said conductor wires; and a passageway extending through a wall of said shell in direct communication with at least one of said base charge and said ignitionprimer charge, and having an area equal to that of a circle having a diameter of from about 0.010 to 0.050".

10. In an electric blasting cap of claim 9 a solid sulfur closure plug in said shell in the end thereof opposite that containing said base charge and superposed on said dielectric plug; said sulfur closure plug being in direct open communication with the outside of said shell; and said leg wires extending through said sulfur closure plug, initially electrically insulated, a portion thereafter in bared contact with said sulfur plug.

11. In an electric blasting cap of claim 10 a metallic cylindrical capsule member, wit-hin, and coaxial with, said shell, superposed on said base charge, and having a reduced diameter at its end farther from said base charge, and said capsule containing a portion of said diazodinitrophenol having a density lower than that of the remaining portion of said diazodinitrophenol so that said diazodinitrophenol outside said capsule is ignitable in response to heat from said bridge wire; and said capsule being formed from a metal dissimilar to that forming said shell.

12. In an electric blasting cap of claim 11, the area of saidpassageway being, equal to that of a circle having a diameter not greater than about 0.025 inch, said shell being formed from aluminum, and said capsule being formed from a metal of the group of bronze and copper.

13. An electric blasting cap of claim- 12, wherein said diazodinitrophenol also contains from l to 3 percent of its weight of a solid acidic material as a corrosion agentforming material together with said sulfur.

14. A complete explosive assembly for use in Water covered areas which comprises an elongated cartridge shell; a cap insensitive explosive blasting composition contained within said shell and iilling substantially all of said shell, and detonatable in response to detonating action of a booster charge described hereinafter; a` booster Well extending into said cartridge shell into contact with said explosive charge therein, and a booster assembly comprising a shell and a cap-sensitive explosive charge contained therein, disposed within said well in indirect detonating relationship with said explosive blasting cornposition; said booster assembly containing a well extending into the shell thereof in direct contact with saidcapsensitive charge in said booster shell; an electric blasting cap assembly within said well in said booster shell, in indirect detonating relationship with said cap-sensitive charge therein; and said electric blasting cap assembly comprising a closed elongated shell; a base explosive charge in one end of said shell disposed therein as described hereinafter; adielectric ignition plug within said shell in closing relationship therewith and spaced from said base charge; a pair of leg wires longitudinally extending into said shell through the end thereof opposite said base charge in direct sealed contact with said dielectric plug, and terminating within said shell intermediate said base charge and said ignition plug; a bridge wire connecting the terminal ends of said leg wires to thereby form an electrical circuit therewith; an ignition composition within said shell in direct contact with said bridge wire; said ignition composition being ignitable in response to heat from said bridge wire developed by passage of electric current through said circuit, and said base explosive charge being disposed in operative communication with said ignition composition to detonate in response to ignition of said ignition composition; a corrosion agent-forming material within said cap assembly chemically inert to all components of said assembly but, upon contact with water, forming an agent corrosive to any of said Wires in said circuit, and present in amount to form said agent in quantity to corrode any of said wires sufficiently to break said circuit; said corrosion agent-forming material being disposed within said assembly so as to permit direct contact of said corrosion agent, when formed, with said circuit for corroding saine as described; ingress means, in said cap assembly for admitting water from outside said shell into contact at a rate, and in an amount, with said corrosion agentforming material to form said agent for said corrosion so as to break said circuit after a preset period oii water ingress time, whereby said blasting cap assembly becomes disarmed.

References Cited UNITED STATES PATENTS 2,739,535 3/1956v Rolland et al. 102-28 2,759,417 8/1956 ONeill 102-28 X 2,945,441 7/1960. Winslow 102--16 3,279,372 10/1966 Patterson 102-28 BENJAMIN A. BORCHELF, Primary Examiner.

V. R. PENDEGRASS, Assistant Examiner. 

1. AN ELECTRIC BLASTING CAP ASSEMBLY CAPABLE OF SELFDISARMING AFTER MISFIRING IN A WATER ENVIRONMENT, WHICH COMPRISES A CLOSED ELONGATED SHELL; A BASE EXPLOSIVE CHARGE IN ONE END OF SAID SHELL DISPOSED THEREIN AS DESCRIBED HEREINAFTER; A DIELECTRIC IGNITION PLUG WITHIN SAID SHELL IN CLOSING RELATIONSHIP THEREWITH AND SPACED FROM SAID BASE CHARGE; A PAIR OF LEGS WIRES LONGITUDINALLY EXTENDING INTO SAID SHELL THROUGH THE END THEREOF OPPOSITE SAID BASE CHARGE IN DIRECT SEALED CONTACT WITH SAID DIELECTRIC PLUG, AND TERMINATING WITHIN SAID SHELL INTERMEDIATE SAID BASE CHARGE AND SAID IGNITION PLUG; A BRIDGE WIRE CONNECTING THE TERMINAL ENDS OF SAID LEG WIRES TO THEREBY FORM AN ELECTRICAL CIRCUIT THEREWITH; AN IGNITION COMPOSITION WITHIN SAID SHELL IN DIRECT CONTACT WITH SAID BRIDGE WIRE; SAID IGNITION COMPOSITION BEING IGNITABLE IN RESPONSE TO HEAT FROM SAID BRIDGE WIRE DEVELOPED BY PASSAGE OF ELECTRIC CURRENT THROUGH SAID CIRCUIT, AND SAID BASE EXPLOSIVE CHARGE BEING DISPOSED IN OPERATIVE COMMUNICATION WITH SAID IGNITION COMPOSITION TO DETONATE IN RESPONSE TO IGNITION OF SAID IGNITION COMPOSITION; A CORROSION AGENT-FORMING MATERIAL WITHIN SAID CAP ASSEMBLY CHEMICALLY INERT TO ALL COMPONENTS OF SAID ASSEMBLY BUT, UPON CONTACT WITH WATER, FORMING AN AGENT CORROSIVE TO ANY OF SAID WIRES IN SAID CIRCUIT, AND PRESENT IN AMOUNT TO FORM SAID AGENT IN QUANTITY TO CORRODE ANY OF SAID WIRES SUFFICIENTLY TO BREAK SAID CIRCUIT; SAID CORROSION AGENG-FORMING MATERAIAL BEING DISPOSED WITHIN SAID ASSEMBLY SO AS TO PERMIT DIRECT CONTACT OF SAID CORROSION AGENT, WHEN FORMED, WITH SAID CIRCUIT FOR CORRODING SAME AS DESCRIBED; INGRESS MANS IN SAID CAP ASSEMBLY FOR ADMITTING WATER FROM OUTSIDE SAID SHELL INTO CONTACT AT A RATE, AND IN AN AMOUNT, WITH SAID CORROSION AGENT-FORMING MATERIAL TO FORM SAID AGENT FOR SAID CORROTION SO AS TO BREAK SAID CIRCUIT AFTER A PRESET PERIOD OF WATER INGRESS TIME, WHEREBY SAID BLASTING CAP ASSEMBLY BECOMES DISARMED. 